An agricultural harvester known as a “combine” is historically termed such because it combines multiple harvesting functions with a single harvesting unit, such as picking, threshing, separating, cleaning, and temporary storage. A combine includes a header which removes the crop from a field, and a feeder housing which transports the crop matter into a threshing drum. The threshing drum rotates within a perforated housing, which may be in the form of adjustable concaves and performs a threshing operation on the crop to remove the grain from the straw. Once the grain is threshed it falls through perforations in the concaves onto a grain pan. From the grain pan the grain is cleaned using a cleaning system, and is then transported to a grain tank onboard the combine. A cleaning fan blows air through the sieves to discharge chaff and other debris, which is also called material other than grain (MOG), toward the rear of the combine. Non-grain crop material such as straw from the threshing section proceeds through a residue system, which may utilize a straw chopper to process the non-grain material and direct it out the rear of the combine. When the grain tank becomes full, the combine is positioned adjacent a vehicle into which the grain is to be unloaded, such as a semi-trailer, chaser bin, straight truck, or the like; and an unloading system on the combine is actuated to transfer the grain into the vehicle.
More particularly, a threshing or separating system includes one or more drums which can extend transversely, in the case of what is known as a “conventional” combine, or axially, in the case of what is known as a “rotary” combine, within the body of the combine, and which are partially or fully surrounded by a perforated concave. The crop material is threshed and separated by the rotation of the drum within the concave. Coarser non-grain crop material such as stalks and leaves are transported to the rear of the combine and discharged back to the field. The separated grain, together with some finer non-grain crop material such as chaff, dust, straw, and other crop residue are discharged through the concaves and fall onto a grain pan where they are transported to a cleaning system. Alternatively, the grain and finer non-grain crop material may also fall directly onto the cleaning system itself.
A cleaning system further separates the grain from non-grain crop material, and typically includes a fan directing an airflow stream upwardly and rearwardly through horizontally arranged sieves which oscillate in a fore and aft manner. The airflow stream lifts and carries the lighter non-grain crop material towards the rear end of the combine for discharge to the field. Clean grain, being heavier, and larger pieces of non-grain crop material, which are not carried away by the airflow stream, fall onto a surface of an upper sieve (also known as a chaffer sieve) where some or all of the clean grain passes through to a lower sieve (also known as a cleaning sieve). Grain and non-grain crop material remaining on the upper and lower sieves are physically separated by the reciprocating action of the sieves as the material moves rearwardly. Any grain and/or non-grain crop material remaining on the top surface of the upper sieve are discharged at the rear of the combine. Grain falling through the lower sieve lands on a bottom pan of the cleaning system, where it is conveyed forwardly toward a clean grain auger.
The clean grain auger conveys the grain to a grain tank for temporary storage. The grain accumulates to the point where the grain tank is full and is discharged to an adjacent vehicle such as a semi-trailer, chaser bin, straight truck or the like by an unloading system on the combine that is actuated to transfer grain into the vehicle.
In conventional combines, where the drum extends transversely, the drum typically has spaced apart slats extending along the width of the drum. The slats rotate in order to contact crop material that has passed through the header and rub the crop material against the concave to thresh and separate the crop material. Due to the geometry and spacing of the slats, there are periods during rotation of the drum that no slats are contacting the entering crop material, i.e., feeding by the drum and slats is discontinuous. When the drum further rotates and one or more of the slats comes into contact with the crop material, a large peak load is created during contact which can lead to rumbling and audible noises in the combine, which reduces operator comfort. Further, the high peak loads can accelerate wear on the slats and are not ideal for power transmission because the irregular power requirements of the drum to discontinuously press crop material against the concave cause cycled, irregular power demand on the power take-off. Similarly, the threshing and separation of the crop material is irregular, which can cause inefficiencies in the separation system and consequently cause inefficient cleaning in the cleaning system. U.S. Pat. No. 2,301,536 A and DE 259 673 C disclose threshing drums with helically arranged threshing slats.
What is needed in the art is a threshing and separating system that addresses some of the previously described disadvantages of known threshing and separating systems.